1. Field of the Invention
The present invention relates to a sheet detecting apparatus that detects the presence or absence of a sheet, and more specifically relates to a sheet detecting apparatus attached to a sheet conveying path of an image forming apparatus such as a copying machine or a printer.
2. Related Background Art
Conventional image forming apparatuses mainly adopt mechanical detection methods as sheet detecting means attached to their sheet conveying paths. As a representative example of the mechanical detecting methods, there has been used a method of a mechanical sensing lever type shown in FIG. 15. With the mechanical sensing lever type method, a lever 201 is arranged so as to block a sheet conveying path.
How the sheet detection of the mechanical sensing lever type is performed will be described. When a leading end portion 30 of a sheet passing through a sheet conveying path presses a part of the lever 201 and the lever 201 is rotated, the lever 201 cuts off a light flux of a photocoupler 202 arranged in proximity to the lever 201. Then, immediately after the sheet has passed therethrough, the lever 201 returns to its original position (indicated by a solid line) due to a force generated by a spring or the like.
When the light flux of the photocoupler 202 is cut off, there is generated a signal for detecting a sheet (there is not shown a signal generating portion). With the generated signal, it becomes possible to detect the presence or absence of a sheet.
However, there is exerted an influence of the counteraction of a spring or the like when the lever 201 returns to its original position, so that there occurs chattering. This chattering results in the increase of a time consumed to detect the trailing end of a sheet with precision. In particular, when a sheet is conveyed at high speed and with precision at constant intervals, it is required to detect the leading end and trailing end of the sheet with precision. As a result, the chattering exerts an enormous influence.
In order to detect the trailing end of the sheet with precision without receiving the influence of the chattering caused with the mechanical detection method, there has been used a detection method that uses an optical sensor. There have mainly been known two types of optical sensors: a reflection type optical sensor shown in FIGS. 16A and 16B and a transmission type optical sensor shown in FIG. 17.
The former reflection type optical sensor has a construction where a light emission element 2154 and a light reception element 2155 are placed on the same substrate and a reflection sheet 205 is affixed to a side opposite to the substrate with a conveying path therebetween, as shown in FIG. 16A. When a sheet 30 does not pass over an optical sensor, irradiation light of the light emission element 2154 is reflected by the reflection sheet and the reflection light is received by the light reception element 2155. While the sheet 30 is passing over the optical sensor, the irradiation light (reflection light) is cut off as shown in FIG. 16B, thereby detecting the sheet.
However, there is a case where erroneous detection is caused by the reflection from the sheet. In order to prevent the erroneous detection, it is required to take measures such as the improvement of the accuracy of the conveying position of each sheet to prevent variations of the position of each sheet or the employment of a condensing lens or the like.
The latter transmission type optical sensor has a construction where the light emission element 2154 and the light reception element 2155 are arranged at positions opposing to each other with the sheet conveying path therebetween, as shown in FIG. 17.
The presence of absence of a sheet is detected by the cutting off of the irradiation light 212 of the light emission element 2154 by the sheet 30. As a result, there occurs no erroneous detection due to the reflection from the sheet 30, but it is required to install the optical sensor with the high accuracy of relative positions on a light emission side and a light reception side.
In recent years, as a modification of the reflection type or transmission type optical sensor, there has been used an optical sensor shown in FIGS. 18A and 18B that combines the advantage of the reflection type with the advantage of the transmission type. This optical sensor has a construction where the light emission element 2154 and the light reception element 2155 are mounted on the same substrate 2152 and the axis of light irradiated from the light emission element 2154 and the axis of light received by the light reception element 2155 are set so as to be parallel through the refraction by a prism 2202 or the like. With this construction, it becomes possible to widen the allowable range of the installation accuracy concerning the light emission element 2154 and the light reception element 2155 and also to reduce the influence of the reflection of the sheet 30.
As shown in FIG. 18A, irradiation light from the light emission element 2154 is refracted twice by a prism 2202 at an incident angle of 45xc2x0 to planes 2203 and 2204 and then is received by the light reception element 2155. While the sheet 30 is passing, the light is cut off and therefore the sheet 30 is detected (FIG. 18B).
In the case of a sheet detection method using an optical sensor, the brightness is increased in accordance with the increase of a current flowing to the light emission element 2154, so that it becomes possible to increase the dynamic range for the sheet detection and to improve the accuracy of the sheet detection. However, if a larger current than is necessary flows to the light emission element 2154, this leads to the reduction of a life span. In contrast to this, if the dynamic range of the optical sensor is set so as to be narrow in consideration of the reduction of the life span, there is increased the influence of stains on a sheet or the sensor, which means that there is a probability that erroneous detection is caused.
With the sheet detection method using an optical sensor, the adjustment of a light quantity of the optical sensor is an important problem. It is required to perform an appropriate initial adjustment when the optical sensor is installed. However, even if the initial adjustment is performed, a light emission portion or a light reception portion becomes dirty due to paper powder of a sheet, dusts adhering to the sheet, or the like, which means that it is required to perform the adjustment of a light quantity at regular intervals or at irregular intervals. As to the timings at which the light quantity adjustment is performed, the intervals between them are set in conformance with light quantity reduction degree due to the speed, specifications, use application, and the like of an image forming apparatus.
Here, a conventional method of adjusting the light quantity of an optical sensor will be described with reference to FIGS. 19A and 19B. FIG. 19A is a graph concerning the adjustment of a light quantity of an optical sensor that is carried out when an image forming apparatus is produced or when the optical sensor is replaced by a serviceman.
The reference symbol Vin represents an application voltage applied to a light emission element of an optical sensor. The reference symbol Vout represents an output voltage obtained by converting the quantity of light received by the light reception element of the optical sensor. When a predetermined voltage is applied to the light emission element of the optical sensor, the light reception element outputs a voltage through a voltage conversion circuit. If the output voltage obtained as a result of this operation is equal to or higher than a preset threshold value Vh, the value is set as a control voltage and the light quantity adjustment is ended.
When there is applied Vin1, an output voltage becomes equal to or higher than the threshold value Vh like in the case of A1 shown in FIG. 19A. Therefore, it is judged that the light quantity adjustment is not required and the adjustment is ended. The threshold value Vh is an output voltage that does not cause any problem concerning the sheet detection even in consideration of the reduction of a light quantity due to the stains on the optical sensor or the life span thereof. This value is set in advance in accordance with the characteristics of the image forming apparatus.
If the output voltage does not reach the threshold value Vh when Vin1 is applied like in the case of B1, the application voltage is gradually increased from Vin1 until there is obtained an output voltage that is at least equal to Vh. Following this, when the output voltage becomes at least equal to Vh, the application voltage (Vin2) is set as the control voltage and the light quantity adjustment is ended.
In the case of C1, like in the case of B1, the application voltage is gradually increased until there is obtained the output voltage that is at least equal to the threshold value Vh. However, if the output voltage does not become at least equal to the threshold value Vh even if, as in the case of C2, the application voltage is increased until VinMAX that is the upper limit value of the application voltage, it is judged that the optical sensor is a defective part.
FIG. 19B is a graph concerning the adjustment of a light quantity of an optical sensor that is performed between jobs like copy jobs or when the power source of an image forming apparatus is turned on.
As shown in FIG. 19B, the light quantity adjustment is performed when the light quantity of the optical sensor is decreased from A1 to A2. The application voltage Vin applied to the optical sensor is increased from Vin1, thereby setting the output voltage at the threshold value Vh or higher. A Vin value (A3) obtained when the output voltage reaches the threshold value is set as the control voltage and the light quantity adjustment is ended.
In a like manner, when the light quantity of the optical sensor is decreased from B2 to B3, the light quantity adjustment is performed. When the output voltage does not become at least equal to the threshold value Vh even if the application voltage applied to the optical sensor is increased to the upper limit value Vin MAX, VinMAX (B4) is set as the control voltage and the light quantity adjustment is ended. It is possible for the optical sensor to perform the sheet detection even if the control voltage is set at VinMAX, although it becomes impossible to perform the sheet detection if the light quantity is decreased to a limit value VS.
There has been avoided the use of the conventional optical sensor at a location where there is easily exerted the influence of paper powder of a sheet or at a location where there is easily exerted the influence of a use environment, so that it has been enough for the judgment of the presence or absence of a sheet that a certain degree of dynamic range is maintained. In addition, by frequently performing the light quantity adjustment between a copy job and another copy job, it becomes possible to perform the adjustment before the light quantity of the optical sensor is significantly decreased. As a result, it has been possible to complete the adjustment in a short time.
However, depending on the performance or use environment of the image forming apparatus, the decreasing degree of the light quantity of the optical sensor becomes considerable, so that it is required to maintain a sufficient dynamic range of an optical sensor. In addition, in an image forming apparatus that is capable of conveying a sheet at high speed, there are performed job copying large quantity of sheets. As a result, the decreasing degree of the light quantity of the optical sensor for one copy job is increased.
If a conventional light quantity adjustment method is adopted under such a circumstance, there is exerted an influence on a time consumed to end the light quantity adjustment. This is because the decreasing degree of the light quantity of an optical sensor is increased and therefore the range of a voltage applied during the light quantity adjustment is increased.
Further, if the decreasing degree of the light quantity of the optical sensor is large, it becomes impossible to perform the sheet detection at a relatively early stage. As a result, an image forming apparatus falls into an inoperable state. In this state, it becomes completely impossible to perform image formation and therefore a user feels dissatisfaction.
An object of the present invention is to provide a sheet detecting apparatus and an image forming apparatus equipped with the sheet detecting apparatus, where the sheet detecting apparatus is capable of performing the most suitable light quantity adjustment under a condition where the quantity of light of an optical sensor is considerably reduced.
Another object of the present invention is to provide a sheet detecting apparatus and an image forming apparatus equipped with the sheet detecting apparatus, where the sheet detecting apparatus is capable of, before it becomes impossible to perform sheet detection, sending a notification to a user, a serviceman, or administrator by displaying the state of an optical sensor.
Still another object of the present invention is to provide a sheet detecting apparatus and an image forming apparatus equipped with the sheet detecting apparatus, where the sheet detecting apparatus is capable of circumventing, as much as possible, a situation where it becomes impossible to perform sheet detection and the image forming apparatus falls into an inoperable state.
Therefore, according to the present invention, there is provided a sheet detecting apparatus, characterized by comprising an optical sensor including a light emission portion and a light reception portion, judging means for judging the presence or absence of a sheet by applying a voltage to the light emission portion adjusting means for adjusting the voltage to be applied to the light emission portion in order to make the judgment, and calculating means for obtaining the voltage to be applied to the light emission portion at the adjusting means through calculation.
Also, according to the present invention, in the sheet detecting apparatus, it is characterized in that when adjusting the voltage to be applied to the light emission portion, the calculating means obtains the voltage to be applied to the light emission portion through calculation based on a relation between a voltage applied to the light emission portion before the adjustment and an output obtained through reception of light from the light emission portion by the light reception portion before the adjustment.
Also, according to the present invention, in the sheet detecting apparatus, it is characterized in that a state of the optical sensor is displayed in accordance with a fact that the voltage obtained by the calculating means is equal to or higher than the maximum value of a voltage applicable to the light emission portion.
Also, according to the present invention, in the sheet detecting apparatus, it is characterized in that the sheet detecting apparatus comprises communication means for communicating with an external apparatus, and that a notification is sent to the external apparatus through the communication means in accordance with a fact that the voltage obtained by the calculating means is equal to or higher than the maximum value of a voltage applicable to the light emission portion.
Also, according to the present invention, in the sheet detecting apparatus, it is characterized in that the adjusting means includes first means for adjusting the voltage to be applied to the light emission portion based on the calculating means and second means for adjusting the voltage to be applied to the light emission portion in accordance with a fact that a predetermined condition is satisfied by an output obtained through reception of light emitted by the light emission portion through gradual application of a voltage, by means of the light reception portion.
Also, according to the present invention, there is provided an image forming apparatus, characterized by comprising a conveying path for conveying a sheet, an optical sensor including a light emission portion and a light reception portion, for detecting a sheet passing through the sheet conveying path, judging means for judging the presence or absence of a sheet by applying a voltage to the light emission portion, adjusting means for adjusting the voltage to be applied to the light emission portion in order to make the judgment, calculating means for obtaining the voltage to be adjusted by the adjusting means through calculation, and control means for controlling conveyance of a sheet by applying the voltage obtained by the calculating means to the light emission portion and by detecting the sheet.
Also, according to the present invention, in the image forming apparatus, characterized in that when adjusting the voltage to be applied to the light emission portion, the calculating means obtains the voltage to be applied to the light emission portion through calculation based on a relation between a voltage applied to the light emission portion before the adjustment and an output obtained through reception of light from the light emission portion by the light reception portion before the adjustment.
Also, according to the present invention, in the image forming apparatus, characterized in that a state of the optical sensor is displayed in accordance with a fact that the voltage obtained by the calculating means is at least equal to the maximum value of a voltage applicable to the light emission portion.
Also, according to the present invention, in the image forming apparatus, it is characterized in that the image forming apparatus further comprises communication means for communicating with an external apparatus, and that a notification is sent to the external apparatus through the communication means in accordance with a fact that the voltage obtained by the calculating means is equal to or higher than the maximum value of a voltage applicable to the light emission portion.
Also, according to the present invention, in the image forming apparatus, it is characterized in that if an output from the light reception portion through the application of the voltage obtained by the calculating means to the light emission portion is equal to or lower than a predetermined value, it is judged that the optical sensor suffers from an abnormality and there is inhibited setting involving use of the sheet conveying path, in which the optical sensor is provided, without inhibiting use of the whole of the image forming apparatus.
Also, according to the present invention, in the image forming apparatus, it is characterized in that an item, whose setting for usage is inhibited, is displayed so as to be distinguishable from each item whose setting is possible, and that setting is not received even if a portion corresponding to the item, whose setting is inhibited, is pushed.
Also, according to the present invention, in the image forming apparatus, it is characterized in that the adjusting means includes: first means for adjusting the voltage to be applied to the light emission portion based on the calculating means, and second means for adjusting the voltage to be applied to the light emission portion in accordance with a fact that a predetermined condition is satisfied by an output obtained through reception of light emitted by the light emission portion emit light through gradual application of a voltage, by means of the light reception portion.
The stated objects and effects of the present invention and other objects and effects thereof will become apparent from description to be made with reference to the following drawings.